Buggy code:
public class EditCommand extends Command { private String name ; private String newName ; private String oldTag ; private String newTag ; int taskId = - 1 ; private ArrayList < Task > taskList = Database . getInstance ( ) . getTaskList ( ) ; private ArrayList < Integer > resultTaskIndexes = new ArrayList < Integer > ( ) ; private Calendar newDeadline ; private Calendar newStartTime ; private Calendar newEndTime ; public EditCommand ( String oldName , String newName ) { } public EditCommand ( String name , Calendar newDeadline ) { } public EditCommand ( String name , Calendar newStartTime , Calendar newEndTime ) { } public EditCommand ( String name , String oldTag , String newTag ) { } public EditCommand ( int taskId , String newName ) { } public EditCommand ( int taskId , Calendar newDeadline ) { } public EditCommand ( int taskId , Calendar newStartTime , Calendar newEndTime ) { } public EditCommand ( int taskId , String oldTag , String newTag ) { } public ArrayList < Task > execute ( ) { <START_BUG> assert ( name ) != null ; <END_BUG> if ( isEditNameWithName ( ) ) { return editNameWithName ( ) ; } else if ( isEditDeadlineWithName ( ) ) { return editDeadlineWithName ( ) ; } else if ( isEditTagWithName ( ) ) { return editTagWithName ( ) ; } else if ( isEditStartTimeWithName ( ) ) { return editStartTimeWithName ( ) ; } else if ( isEditEndTimeWithName ( ) ) { return editEndTimeWithName ( ) ; } else if ( isEditNameWithId ( ) ) { return editNameWithId ( ) ; } else if ( isEditDeadlineWithId ( ) ) { return editDeadlineWithId ( ) ; } else if ( isEditTagWithId ( ) ) { return editTagWithId ( ) ; } else if ( isEditStartTimeWithId ( ) ) { return editStartTimeWithId ( ) ; } else if ( isEditEndTimeWithId ( ) ) { return editEndTimeWithId ( ) ; } else { return null ; } } private boolean isEditEndTimeWithName ( ) { } private boolean isEditStartTimeWithName ( ) { } private boolean isEditTagWithName ( ) { } private boolean isEditDeadlineWithName ( ) { } private boolean isEditNameWithName ( ) { } private boolean isEditEndTimeWithId ( ) { } private boolean isEditStartTimeWithId ( ) { } private boolean isEditTagWithId ( ) { } private boolean isEditDeadlineWithId ( ) { } private boolean isEditNameWithId ( ) { } private ArrayList < Task > editEndTimeWithId ( ) { } private ArrayList < Task > editStartTimeWithId ( ) { } private ArrayList < Task > editTagWithId ( ) { } private ArrayList < Task > editDeadlineWithId ( ) { } private ArrayList < Task > editNameWithId ( ) { } private ArrayList < Task > editEndTimeWithName ( ) { } private ArrayList < Task > editStartTimeWithName ( ) { } private ArrayList < Task > editTagWithName ( ) { } private ArrayList < Task > editDeadlineWithName ( ) { } private ArrayList < Task > editNameWithName ( ) { } private ArrayList < Task > editDeadline ( ) { } private ArrayList < Task > editName ( ) { } private ArrayList < Task > editTag ( ) { } private ArrayList < Task > editEndTime ( ) { } private ArrayList < Task > editStartTime ( ) { } private void searchWithName ( ) { } private void searchWithId ( ) { } private ArrayList < Task > withIdToWithName ( ArrayList < Task > result ) { } }

Fix:
assert ( ( name ) != null ) || ( ( taskId ) != ( - 1 ) ) ;